1. Field
Embodiments of the invention generally relate to an RF delivery system in a semiconductor substrate processing apparatus and the like.
2. Description of the Related Art
The demand for faster, more powerful integrated circuits (IC) devices has introduced new challenges for IC fabrication technology, including the need to etch submicron features on a substrate, such as a semiconductor wafer, with a good uniformity across the substrate. For example, deep trench storage structures used in some dynamic random access memory applications require deep high aspect ratio trenches to be etched into a semiconductor substrate. Deep silicone trench etching is typically carried out in a reactive ion etching (RIE) process.
FIG. 1 depicts a conventional processing chamber 100 utilized for etching material layers disposed on a substrate 144 to form features therein. The processing chamber 100 has a substrate support assembly 148 disposed in an interior volume 106 of the processing chamber 100. The substrate support assembly 148 includes an electrostatic chuck 166, a base plate 164 and a facility plate 190. The base plate 164 and the facility plate 190 are electrically insulated by an insulating material 192 disposed therebetween. Alternatively, a gap or a space may be defined between the base plate 164 and the facility plate 190 to provide electrical insulation. A dielectric insulator ring 120 may be attached to an edge of the facility plate 190. The electrostatic chuck 166 and the base plate 164 are generally formed from ceramic or similar dielectric materials. A heating element 176 is disposed in the electrostatic chuck 166 or the base plate 164 and is utilized to control the temperature of a substrate disposed on the substrate support assembly 148. The heating element 176 is coupled by wires disposed in a center region of the substrate support assembly 148 to a heater power source 178.
At least one clamping electrode 180 is disposed in the electrostatic chuck 166 or the base plate 164. The clamping electrode 180 is coupled to a chucking RF power source 164 through the center portion of the substrate support assembly 148. An RF electrode 182 disposed in one of the electrostatic chuck 166 or base plate 164 is coupled to one or more RF power sources 184, 186 through a matching circuit 188 through an RF transmission line 150 to maintain a plasma in the processing chamber 100. The RF transmission line 150 is disposed through the substrate support assembly 148 in a location that is offset from a center axis of the substrate support assembly 148. The RF transmission line 150 is utilized to transmit RF power supplied from the RF power sources 184, 186 to the RF electrode 182. Since some substrate support utilities occupy the space along the central axis of the substrate support assembly 148, the RF transmission line 150 is coupled to a metal plate 154 disposed in the substrate support assembly 148. The metal plate 154 is utilized to conduct the RF power from the offset RF transmission line 150 to a central feed through 152 routed through the center of the substrate support assembly 148.
Typically, it is desired to apply RF power to the substrate surface in a manner that produces a uniform electric field across the substrate surface to promote plasma uniformity. Uniform distribution of the electric field and dissociated ion plasma across the substrate surface provides uniform etching behavior across the substrate surface. In order to maintain uniform electric field and plasma distribution, it is desired that the RF power is supplied to the substrate through a center region of the processing chamber, e.g., either through a showerhead electrode and/or through a substrate support electrode. As discussed above, the center portion of the substrate support assembly 148 is occupied by utilities and/or routing a shaft utilized to actuate lift pins (not shown). The RF transmission line 150 needs to be offset from the center of the substrate support assembly 148. Accordingly, in conventional configurations, the RF transmission line 150 is typically coupled to the base plate 164 at a position offset to the center axis of the substrate support assembly 148. The metal plate 154 is therefore utilized to carry the RF power from the offset RF transmission line 150 to the center region of the substrate support assembly 148 through the center conduit 152 disposed therein.
As the top portion 156 of the RF transmission line 150 is directly below the facility plate 190 at a region 158 offset to the center axis of the substrate support assembly 148, the electric field generated around the region 158 is particularly different from other regions outward from the contacted region 158. For example, in the region 158 directly above the RF transmission line 150, the electric field is typically weaker than the electric field spread out in other regions where the RF transmission line 150 is adjacent but not directly below. The offset the RF transmission line 150 often results in non-uniform electric field, thereby creating a skew pattern of the electric filed across the substrate surface.
FIG. 2 depicts an electric field distribution measured across the surface of the substrate 144 positioned on the substrate support assembly 148 while applying an RF power thereto. The electric field in the region 158 where the RF transmission line 150 is positioned is comparatively weaker than the electric fields in other regions 160 across the substrate, resulting in the undesired skew of the electric field. Skew of the electric field contributes to non-uniform ion dissociation and plasma distribution across the substrate surface, thereby causing in poor etching uniformity.
Therefore, there is a need for an improved apparatus for providing uniform electric field distribution across a substrate surface.